SOLID VITREOUS CARBON

Vitreous carbon can be produced in the fonn of an open-pore foam, known as reticulated vitreous carbon (RVC). The precursor materials are essentially the same polymers used for solid vitreous carbon, except that they are foamed prior to carbonization. The carbonization process is similar. The open-pore structure of the material is shown in Fig.6.8.i l... 

Solid electrodes in unstirred solution. The most useful solid electrodes are platinum, gold, vitreous carbon, and carbon paste. The preferred configuration for theoretical work is a flat planar surface sealed in glass with epoxy or snugly fitted into a Teflon shroud. The electrodes ordinarily are unshielded, although shielded designs have been described.94... 

The encapsulation of catalytically active species into porous solids is one of the possible strategies of particular interest. Thus, Bessel and Rolison (1997b,c) compared the electrocatalytic effect of zeolite Y-encapsulated Co(salen) (salen = N,N -bis(salicylidene)ethylenediamine) on the reaction between benzyl chloride and carbon dioxide in tetrahydrofuran/hexamethylphosphoramide, with that exerted by the same complex in solution. Using a large surface area reticulated vitreous carbon electrode immersed into suspensions of Co(salen) NaY in solutions of the reagents, the effective electrocatalytic turnover is ca. 3000 times that of homogeneous Co(salen) under comparable conditions. Remarkably, coulometric experiments indicated that only... 

Awad, M.L, Saleh, M.M., and Ohsaka, T. 2008. Oxygen reduction on rotating porous cylinder of modified reticulated vitreous carbon. Journal of Solid State Electrochemistry 12, 251-258. 

Tantalum, which is used for a number of applications, was recently made into a porous material that could be used for bone reconstruction. The porous structure is made by depositing the metal onto a vitreous carbon scaffold using chemical vapor deposition/infiltration techniques. Its low stmctural density means that its stiffness (2.5-4 GPa) is closer to that of natural bone than the solid metal, and the porosity means that bone can fully integrate into the stmcture. forming an excellent bond. " ... 

Lewis, J.C. and Redfern, B., and Cowland, F.B. (1963). Vitreous Carbons as Crucible Materials for Semiconductors. In Solid State Electronics, 6, 251. 

Most commonly, the battery will be configured with a stack of bipolar cells (10 -100 cells per stack) to give a useful output voltage and with parallel flows for the electrolytes to each of the cells in the stack. Hence, the electrodes will be bipolar with a solid core from carbon, graphite, or a carbon/polymer composite and the three-dimensional elements bonded or pressed onto either side of the solid core. The composites are a blend of a chemically stable polymer and a micron-scaled carbon powder, most commonly an activated carbon Radford et al. [127] have considered the influence of the source of the carbon and the chemical and thermal treatments on the properties of such activated carbons, especially the pore size and distribution [126]. Even though reticulated vitreous carbon has been used for the three-dimensional elements [117], the predominant materials are graphite cloths or felts with a thickness of up to 5 mm, and it is clear that such layers are essential to scale the current density and thereby achieve an acceptable power density. Details of electrode performance in the more developed flow batteries are not available but, for example, Skyllas-Kazacos et al. [124] have tabulated an overview of the development of the all vanadium redox flow battery that includes the electrode materials and the chemical and thermal treatments used to enhance activity and stability. 

More recently, Llobet and coworkers reported the anodic electropolymerization of A -substituted pyrroles as a convenient method of anchoring a redox-active dinuclear ruthenium catalyst onto conducting solid supports, like vitreous carbon sponges (VCS) and fluorine-doped tin oxide (FTO). In the presence of Ce(IV) as the sacrificial oxidant, turnover numbers up to 76 have been achieved. A major improvement of the system is accomplished by the copolymerization with a robust non active redox species, able to further separate the catalytically active species on the solid support, obtaining up to 250 catalytic cycles. 

Vitreous carbon can be produced in three basic types which have essentially the same microstructure, but different macrostructures solid (or monolithic), foam (or reticulated), and spheres (or particles). Each type is reviewed in the next three sections. 

Hlgh>Temperature Thermal Insulation. A potential application of vitreous-carbon foam is high-temperature thermal insulation in vacuum or non-oxidizing atmosphere. Severai factors combine to make this structure an exceiient thermal insulator (a)Vne low volume fraction of the solid phase, which limits conduction (b) the small cell size, which virtually eliminates convection and reduces radiation through repeated absorption/reflection at the cell walls and (c) the poor conductivity of the enclosed gas (or vacuum). An additional advantage is its excellent thermal-shock resistance due to its... 

A typical process for the production of vitreous-carbon spheres is represented schematicctlly in Fig. 6.9.1 The precursor is a partially polymerized polymer such as furfuryl alcohol, catalyzed with p-toiuene sulfonic acid and mixed with acetone to obtain the proper viscosity for atomization.l l A pore former is added which can be an organic material with a high boiling point or sub-micron solid particles such as carbon black. Atomization occurs in the thermal reactor shown schematically in Fig. 6.10.1 The curing time is very brief because of the small size of the particles ( 45jum). 

A PT-modified vitreous carbon electrode can be used as a universal response potentiometric sensor. This all-solid-state electrode is readily prepared, responds rapidly, and has good stability and reproducibility [798]. A potentiometric iodide sensor based on a PMT film electrode has been developed. This... 

The situation is somewhat different with solid electrodes several materials are used here such as platinum, gold, as well as different types of carbon materials, e.g., glassy (vitreous) carbon etc. All these solid electrodes are particularly convenient in... 

Solid substrate electrodes (platinum, gold, vitreous carbon) with electrochemically deposited 3-octylthiophene is seen as a coated electrode with an ion-selective membrane to produce a solid-contact ion-selective electrode for several ions (e.g. Li+, Ca +, C [209]. 

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